Ultrasonic methods and systems may be used to measure the concentration and other properties of suspended particles or other materials, including, for example, biologic materials. For example, there is a need to measure concentration of human islets in preparations for human transplantation. These measurements can be combined with separate measures of the viability of the islets to determine the number of viable and dead cells in a preparation. There is also a need for systems that can measure properties of small particles on a nanoscale.